Printer for continuous form with justification control

ABSTRACT

A justification system is provided for use in an electrophotographic printer. The justification system comprises a detector which detects the passage of individual segments of a continuous form which are being fed at a predetermined rate. A counter counts the number of main scannings of a laser beam carrying printing information over the surface of a photoconductive drum. A read control is connected to the detector and the counter and controls reading of main information stored by monitoring outputs from the detector and the counter so that printing of each segment always occurs at a predetermined position, synchronously with passage of the segments.

.Iadd.

This application is a reissue of U.S. Pat. No. 4,870,434 issued Sep. 26,1989. .Iaddend.

BACKGROUND OF THE INVENTION

This invention relates to a printer which prints information on acontinuous form by transferring toner images thereonto, and moreparticularly to a justification system for controlling printing inaccordance with the rules on the continuous form.

Conventionally, there is known an image recording device utilizing aso-called electrophotographic system in which a surface of aphotoconductive drum is exposed to light to form a latent image on thedrum surface, toner is then applied to the latent image to develop theimage, and the developed image is transferred onto a recording sheetmaterial and is fixed by a fixing unit. Such an image recording deviceis chiefly employed in a copying machine. In recent years, however,image recording devices have been utilized in printers and the like forprinting out output from a computer.

In a copying machine, in general, cut sheets are used as the recordingsheet material, and a heat-roll fixing system is utilized wherein thetoner is fixed by heat as well as pressure. In addition, a pressurefixing system has recently been developed, which is low in electricpower consumption and which does not require an undue amount of time forpreheating the heat rolls.

In the printer, however, it is desired to use, as the recordingmaterial, a continuous recording form which is .[.form.]. identical withthat used in a conventional line-printer; the continuous recording formidentical to the conventional one is a folded continuous recording form(hereinafter referred to simply as "continuous form"), called afan-folded form, which has formed therein sprocket holes. Perforationsare provided between each of the folded sections to enable sheetsections to easily be severed from each other. Horizontal rules aremarked at predetermined intervals in a longitudinal direction betweenthe perforations, with a predetermined positional relationshiprespective to the sprocket holes.

In the above printer, a continuous form having carried thereon unfixedtoner image is clamped and passed between a pair of rotating fixingrolls so that the toner image is fixed onto the continuous form. Thecontinuous form is driven to travel by, for instance, rotation of thefixing rolls.

In the meantime, the printer employing the fan-folded form defines anon-printing area around the perforations because the form is cut intopieces of paper at the perforations after printing.

In the printer described above, however, expansion or contraction of thecontinuous form due to humidity, variation in the diameter of the fixingrolls, change in the thickness of the continuous form at the fixingrolls, and so on, cause printable segments of the continuous form to beout of phase with the associated area of the circumferential peripheralsurface of the photoconductive drum, relative to rules.

Further, motors utilized for scanning the photoconductive drum and theexposure system are varied in their rpm (revolutions per minute) due tothe variation in supply voltage and their age. Thus, even if eachprinting segment of the continuous form is fed at a constant rate, theassociated area of the photoconductive drum is shifted out of positionand thereby the printing position is slipped away from the rules,resulting in a poor impression.

Moreover, the continuation of printing accumulates such errors, makingthe rules meaningless. In the worst case, the printing occurs atnon-printing areas around the perforations.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a justificationsystem for use in an electrophotographic printer, employing a continuousform.

For the above purpose, according to the invention, there is provided ajustification system for use in an electrophotographic printer in whichthe surface of a photoconductive drum is main scanned in a direction ofthe axis of the drum, and in which electrophotographic printing occurson a continuous form which is fed at a predetermined rate by a feedmechanism and provided with a plurality of print segments, saidjustification system comprising:

detector means for detecting passage of end of each segment of saidcontinuous form;

counter means for counting the number of said main scannings on saidphotoconductive drum, starting with the passage of said end of each saidsegment;

storage means for storing printing information; and control means forcontrolling the reading of the printing information from said storagemeans on the basis of the number of said main scannings as counted bysaid counter means, and passage of the end of each said segment asdetected by said detector means, in such a manner that the printing onsaid continuous form always occurs at a preselected position withrespect to each said segment.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a side view of a printer with a justification system embodyingthe invention;

FIG. 2 is a diagrammatic perspective view showing principal parts of theprinter;

FIG. 3 is a functional block diagram of the justification system; and

FIGS. 4 through 7 are time charts of the signals in FIG. 3 in differentsituations.

DESCRIPTION OF THE EMBODIMENTS

Referring to FIGS. 1 and 2, there is illustrated a laser beam printer,in which a fan-folded form 10 is used as a continuous recording form,and in which a justification system embodying the invention isincorporated. The laser beam printer is designed to print outinformation fed from a computer or the like, not shown, onto thefan-folded form 10 by means of an electrophotographic system.

The laser beam printer comprises a photoconductive drum 1. Arrangedabout the photodetective drum 1.Iadd., .Iaddend.in order in therotational direction thereof indicated by the arrow in FIG. 1, are atoner-cleaning station 2, a decharging station 3, a charging station 4,an optical scanning system 5 for directing a laser beam modulated on thebasis of inputted information to the photoconductive drum 1, adeveloping station 6, and a transferring station 7. A fixing station 8is arranged downstream of the photoconductive drum 1 with reference tothe traveling direction in which the fan-folded form 10 travels along apredetermined path. A direction-regulating feed mechanism 9 is arrangedin the predetermined path and at a location between the photoconductivedrum 1 and the fixing station 8.

The optical scanning system 5 comprises a semiconductor laser 61, acollimator lens 52, a beam shaper 53, a polygonal mirror 54, .[.and.]..Iadd.an .Iaddend.F lens 55, and a reflecting mirror 56. The beamemission of the semiconductor laser 61 is regulated by a laser beammodulating circuit 41. A modulating signal Sv is fed into the beammodulating circuit 41 from an image information generating circuit 40,into which a signal Sv is fed from a host computer, not shown.

The arrangement is such that the laser beam from the optical scanningsystem 5 scans the charged surface of the drum 1 along an axis thereofto carry out a main scanning, and the drum 1 is rotated to carry out anauxiliary scanning, to thereby form a latent image on the charged drumsurface. Toner is then applied at the developing station 6 to the latentimage to develop the same. Subsequently, the developed toner image istransferred at the transferring station 7 onto the fan-folded form 10driven to travel by the mechanism of the fixing station 8 at a velocityidentical with the peripheral speed of the photoconductive drum 1. Thetransferred toner image on the fan-folded form 10 is fixed at the fixingstation 8. The fan-folded form 10 carrying the fixed image thereon isdischarged out of the printer.

At the fixing station 8, a fixing roll pair 81 is arranged which iscomposed of a pair of upper and lower pressure rolls .[.81A.]. .Iadd.81B.Iaddend.and .[.81B.]. .Iadd.81 A .Iaddend.having their respective axesextending perpendicularly to the traveling direction of the fan-foldedform 10. A gap defined between outer peripheral surfaces of therespective upper and lower pressure rolls 81A and 81B of the fixing rollpair 81 is set so that when the fan-folded form 10 is clamped betweenboth of the pressure rolls 81A and 81B, the fan-folded form 10 ispressurized with a predetermined pressure.

The upper pressure roll 81B is drivingly connected to a drive motor 20through a chain (not shown). The upper pressure roll 81B is rotatablydriven by the drive motor 20 to clamp the fan-folded form 10, .[.havingcarried.]. .Iadd.carrying .Iaddend.thereon an unfixed image.[.,.].between the upper and lower pressure rolls 81B and 81A. The upper andlower pressure rolls 81B and 81A cooperate with each other to pressurizethe fan-folded form 10 to squeeze the unfixed image thereon, therebyfixing the image onto the fan-folded form 10. This is called apressure-fixing system. The upper and lower pressure rolls 81B and 81Aalso cooperate with each other to drive the fan-folded form 10 to travelalong the predetermined path, to discharge the fan-folded form 10,carrying thereon the fixed image, out of the printer.

The peripheral speed of the photoconductive drum 1 is brought completelyinto .[.concidence.]. .Iadd.coincidence .Iaddend.with that of thepressure roll pair 81. That is, the fan-folded form 10 is driven totravel at a transport velocity corresponding to the peripheral speed ofthe pressure roll pair 81.

Meanwhile, a heat roll fixing system may, of course be adopted insteadof the pressure fixing system in this embodiment.

The direction-regulating feed mechanism 9 comprises a pair of endlesstension belts 91 and 91 which are arranged, respectively, below theopposite side edge portions of the fan-folded form 10, which travelsfrom the transferring station 7 towards the fixing station 8 along thepredetermined path. The tension belts 91 and 91 extend parallel to thetraveling direction.

Each of the tension belts 91 .[.comprise.]. .Iadd.comprises .Iaddend.aso-called synchronous belt provided on an inner peripheral surface witha plurality of teeth so as to mesh with pulleys 92A and 93A. Each of thetension belts 91 is further provided on an outer peripheral surface witha plurality of projections 91A which are arranged in a single row alongthe entire periphery of the tension belt 91. The projections 91A on eachtension belt 91 are spaced from each other at intervals of 1/2 inchequal to that of the sprocket holes 10A formed along a corresponding oneof the opposite side edges of the fan-folded form 10, so that theprojections 91A are engageable, respectively, with the sprocket holes10A as shown in FIG. 2.

In the meantime, the projections 91A are spindle shaped, facilitatingengagement with the sprocket holes 10A.

The tension belt 91 extends between two parallel pulleys 92A and 93Amounted on shafts 92 and 93, perpendicular to the feed direction of thefan-folded form 10. The upper path of the belt 91 coincides with thepath of the fan-folded paper 10.

A power clutch 31 is coupled to one end of the shaft 92, causing theshaft 92 to rotate with a predetermined torque. A rotary encoder 13,serving as a detector for detecting the passage of the end of eachpredetermined segment of the fan-folded form 10, is coupled to theopposite end of the shaft 92 through a pulley 92B and a belt 13A. Therotary encoder 13 is adapted to produce a signal in synchronism with theprojections 91A on the tension belt 91, generating one pulse each timethe projection 91A passes by a certain point in its cyclical path.

Since the projections 91A on the tension belt 91 mesh with the sprocketholes 10A of the fan-folded form 10, the output signal of the rotaryencoder 13 corresponds to the pitch of the sprocket holes 10A in thefan-folded form 10. In view of the predetermined relationship of thepitch of the sprocket holes 10A of the fan-folded form 10 with the rulesprovided thereon (in the embodiment, two pitches of the sprocket holes10A of the fan-folded form 10 are assigned one inch, for which there arefour rules so as to divide the one inch segment into three equal parts),and the output signal of the rotary encoder 13 is thus rendered to be insynchronism with the rules on the fan-folded form 10. The output signalof the rotary encoder 13 will be referred to simply as PFS (Paper FeedSignal) hereinunder.

The pulley 92A is coupled to the shaft 91 through a one-way clutch, notshown, which allows the pulley 92A to rotate with the shaft 92 in thefeed direction171 ,.]. of the fan-folded form 10 but .Iadd.which.Iaddend.prevents shaft 92 from rotating in the reverse direction, withonly the pulley 92A being idled.

The pulley 93A is rotatably mounted on the shaft 93.

There is provided a BD (Beam Detecting) sensor 57 which produces ahorizontal synchronous signal when the laser beam main-scans thephotoconductive drum 1, and which may comprise a photodetector disposedin the path of the main scanning at a position which is a predetermineddistance away from the end of the photoconductive drum 1 in its axialdirection. A pulse start-write control signal, i.e..Iadd., .Iaddend.ahorizontal synchronous signal (referred to as simply "Hsync"hereinafter) is generated after the BD sensor 57 receives the laserbeam. The number of main scannings may be obtained by counting thesignal pulses.

Referring now to FIG. 3, there is shown a block diagram of ajustification system to correct the position of printing on thecontinuous form.

The justification system comprises a page memory M serving as means forstoring printing information to be printed by the laser-beam printer,and a read control 51 (the portion enclosed by a dotted block as shownin FIG. 3) serving as means for controlling reading from the page memoryM.

The page memory M stores a page of text information, and is addressed bythe read control .[.61.]. .Iadd.51 .Iaddend.to output the textinformation as a laser video signal to a laser modulator on a singlemain-scanning basis. When the current page has been read out, thecontents of the page memory M are referred to the next page for the nextreading.

The semi-conductor laser 61 is switched by a laser beam modulator, notshown, to produce a modulated laser beam carrying printing information.

Using, for example, 120 DPI (dots per inch) as the number ofmain-scannings of the laser beam on the photoconductive drum 1, asmeasured in the direction of the auxiliary scanning, and configuring acharacter to be printed with 20 by 20 dots, then the size of onecharacter is approximately 2.54 mm (height) by 1.69 mm (width).

By way of example, a print format is chosen in such a manner that a pageof the fan-folded form 10 in the embodiment (a page is defined by thearea extending between adjacent perforations) is printed with 62 linesby 96 characters. The two uppermost lines and the two lowermost linesare, however, used for margins because of 1/6 inch per line.

Hence, the number of X addresses in the page memory M will be 1920 (96character by 20 dots) and the number of Y addresses will be 1240 (62lines by 20 dots). What is required for the read control 51 is tospecify X and Y addresses, timely reading the information on a singlemain scanning basis, so as to maintain the relationship between therules and the resultant printing on the fan-folded form 10.

Therefore, the read control 51 is arranged as follows:

X address is specified by a counter 51X having a clock input coupled tothe master clock video signal frequency and a reset input coupled toHsync. Thus, a counter 51X outputs 1920 addresses during the period ofthe horizontal synchronization.

A Y address is specified by a combination of two counters, 51y and 51Yand an AND gate 51G.

The counter 51y, has a clock input coupled to Hsync and a reset inputcoupled to an output signal S1 from AND gate 51G. The counter 51y has anadditional output to provide a signal (referred to as 57S hereinafter)each time 57 counts of clock pulses Hsync have been reached.

The counter 51Y has a clock input coupled to signal S1 from AND gate51G, and a reset input coupled to a page signal produced from PFS.

AND gate 51G performs a logic AND of PFS and 57S from the counter 51y,and supplies an output signal S1 to the clock input of the counter 51Yand the reset input of the counter 51y.

The outputs of the two counters 51y and 51Y specify Y addresses of thepage memory M totaling 171 number of.]. .Badd.1240.

The read control 51 arranged as stated assures that the information inthe page memory M is timely read out to maintain the relationshipbetween the printing and the rules on the fan-folded form 10.

The operation of the read control 51 will now be described by referringto timing charts for the signals PFS, Hsync, 57S and S1.

FIG. 4 is a time chart illustrating a situation in which all signalsoccur at normal times. In this case, PFS, the signal from the rotaryencoder 13, has a pulse repetition rate of one pulse per 1/2 inchmovement of the fan-folded form 10. There should be 60 pulses of Hsyncduring the period of PFS. This is because 4 rules are marked per 2pitches (1 inch) of the sprocket holes .Iadd.10A .Iaddend.thereby.[.10A.]. of the fan-folded form 10, dividing the 1 inch area into threeequal parts, with 2 lines printed between adjacent rules. So, 6 linesare printed per 2 pitches (1 inch) of the holes 10A, rendering 3 linesto be printed per 1 pitch (1/2 inch) of the holes 10A. Since the size ofone character is 20×20 dots, the number of dots per 3 lines is 60, whichmatches the number of pulses of Hsync. The counter 51y specifies Yaddresses for the above 3 lines.

In the dot matrix of printing characters, a 16 by 16 dot area isallocated where .[.a.]. characters .[.is.]. .Iadd.are .Iaddend.actuallyprinted, and the remaining area is allocated as space. Thus, 56 dots(20+20+16) completes the 3 line printing. Therefore, signal 57S (56 dotsplus 1 dot) is utilized to indicate when Y addressing for the 3 linescovering the characters is completed.

Since AND gate 51G performs a logical AND of 57S and PFS, the outputsignal S1 is inhibited until at least the 57 dot printing has beencompleted. Thereafter, the signal S1 is enabled to initialize thecounter 51Y so as to specify the Y address corresponding to thebeginning of the next three lines. In this manner, the counter Ycontinues the process in which it specifies the start on base Y addressfor each of 3 line segments upon receiving signal S1 occurring atintervals of 3 lines, and is reset upon receiving the page signal inpreparation for printing of the next page.

FIG. 5 shows a situation in which the fan-folded form 10 is expanded.

In this case, the interval of pulses of PFS is lengthened, depending onthe expansion of the fan-folded form 10. Therefore, the counter 51y isallowed to scan Y addresses covering 3 lines. Since the addressing ofthe start Y address of the next 3 lines is deferred until the next PFSis supplied, the start position of the next 3 lines is corrected,through the spacing between lines is enlarged when going from the lastline of 3 lines to the first line of the next 3 lines. The clock signalS1 is supplied timely to the counter 51Y to assure that this occurs.

FIG. 6 shows a situation in which the fan-folded form 10 is contracted,but in which the space for 3 line printing is still allowed to cover 57dots to be printed.

Although the pulse interval of PFS is shortened depending upon thecontraction of the fan-folded form 10, there is sufficient space in thiscase for the printing of 57 dots .[.or.]. .Iadd.of .Iaddend.characterinformation. Thus, the counter 51y is forcibly reset by the signal S1from AND gate 51G to specify the Y address for the next 3 lines. At thesame time, the signal S1 directs counter 51Y to point to the startaddress of the next 3 lines. In this manner, the correction is made inthe printing position, though the spacing between the lines is narrowedwhen going from a 3 line segment to the next segment.

FIG. 7 shows a situation in which the fan-folded form 10 is furthercontracted so that the space for the 3 line printing cannot cover 57dots.

Since the signal S1 from AND gate 51G is inhibited until the signal 57Sis supplied, it will be enabled upon the next PFS to increment thecounter 51Y, which, in turn, specifies the start Y address of the next 3lines. Therefore, .[.the.]. printing information is printed beyond.Iadd.the .Iaddend.current segment for the 3 l line printing. The next 3line printing starts in synchronism with the next PFS, disregarding onePFS. Hence, the 3 line printing does not occur at the segment which wasin the reach of the previous 3 line printing. This control is used topreserve the print information and to correct the printing position.

In practice, it will be unnecessary to consider the situation in FIG. 7,because the fan-folded form 10 does not contract so much due to theproperties of fan-folded forms, although it can expand considerably.

In this manner, the justification system is capable of correction forpositional errors in printing due to expansion or contraction of thefan-folded form 10.

Even if the feed rate of the continuous form is maintained at a constantspeed, positional printing errors can occur, arising from variations inrpm of the motors for scanning the photoconductive drum 1 and theexposure system due to fluctuations in supply voltage, aging, etc. Insuch cases, PFS is constant but Hsync is subject to variations. Thejustification system similarly operates to correct printing errorsbecause the system may be regarded as providing relative control betweenPFS and Hsync.

Regardless of the above-described features, photo detectors ormicro-switches may be used to detect the passage of the end of eachsegment of the continuous stationery.

What is claimed is:
 1. A justification system for use in anelectrophotographic printer in which the surface of a photoconductivedrum is main-scanned in a direction of the axis of the drum and in whichelectrophotographic printing occurs on a continuous form which is fed ata predetermined rate by a feed mechanism, said form being provided witha plurality of print segments, said justification systemcomprising:detector means for detecting passage of an end of eachsegment of said continuous form; counter means for counting the numberof main scannings on said photoconductive drum, starting with thepassage of said end of each said segment; storage means for storingprinting information; and control means for controlling the reading ofprinting information from said storage means on the basis of said numberof said main scannings as counted by said counter means and passage ofthe end of each said segment as detected by said detector means in sucha manner that printing on said continuous form always occurs at apreselected position with respect to each said segment.
 2. The systemaccording to claim 1, wherein said control means is operable to initiatereading of the printing information synchronously with the passage ofeach said segment.
 3. The system according to claim 1, wherein saidcontrol means is operable, when the output of said counter meansindicates that printing has been completed with respect to a segmentbefore the passage of the leading end of the next segment is detected bysaid detector means, to initiate reading of the print information foreach said next segment upon the detection of the passage of the leadingend of each said next segment.
 4. The system according to claim 1,wherein said detector means comprises a rotary encoder coupled to atension mechanism for subjecting said continuous form to tension, saidtension mechanism being driven in accordance with the movement of saidcontinuous form.
 5. The system according to claim 1, wherein saidsegments correspond to the pitch of sprocket holes formed along oppositesides of said continuous form. .Iadd.
 6. A justification system for usein an electrophotographic printer in which the surface of aphotoconductive drum is main-scanned in a direction of the axis of thedrum and in which electrophotographic printing occurs on a continuousform which is fed at a predetermined rate by a feed mechanism, said formbeing provided with a plurality of print segments, said justificationsystem comprising:means for monitoring the relationship of each segmentof said continuous form and a predetermined area on said drum; means forprinting information on said continuous form; and means for controllingprinting in such a manner that printing on said continuous form alwaysoccurs at a preselected position with respect to each saidsegment..Iaddend. .Iadd.7. A justification system in accordance withclaim 6, wherein said means for controlling printing comprises means forcorrecting for positional errors in printing on said form, based uponsaid relationship..Iaddend.